Repeater for multiplex systems



July 7, 1925. 1,544,910 f B. W. KENDALL REPEATER FOR MULTIPLEX SYSTEMS Filed Got. 51, 1919 I, Bar/0n V14 Kendafl Patented July 7, 1925.

UNITED 8 TE 1,53% PATENT BURTON W. KENDALL, OE NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COM PANY, INCORPORATED, OF NEW YORK, N. Y., A CGRPOB-ATIO'N 0F NEW YORK.

EEPEATER FOR MUL'I'IPLEX SYSTEMS.

Application filed October 31, 1919. Serial No. 334,681.

1 '0 all whom it may concem:

.Be it known that I, BURTON W. KEN- D ALL, a citizen of the United States, residin at New York, in the county of New 5 York, State of New York, have invented certain new and useful Improvements in Repeaters for Multiplex Systems, of which the following is a full, clear, concise, and exact description.

This invention relatesto multiplex signaling systems, and particularly to a repeater .for such systems which is both simple and efficient. The invention is especially concerned with repeating a plurality of telephone conversations or telegraphic messages simultaneously, which several conversations or messages may be in the form of modulations of as many dififerent-carrier waves on asingle transmission line. Broadly, however, the invention is not limited to signalingbut is adapted for use in repeating for,

any purpose currents covering a large frequency-range.

Heretofore it has been thought necessary in order to repeat a plurality of carrier waves, each modulated in accordance with signals, to separate the several carrier waves and repeat the wave of each frequency by itself, afterward recombining tlrefrequencies in the outgoing line. requires the use of considerable apparatus, including more or less complicated filters.

According to the present invention all the frequencies that are being transmitted over the line in the same direction are repeated by a single repeater especially adapted for this purpose, and a twoway repeater may be provided by duplicating the circuit to provide a path for operation in the opposite direction.

A repeater suited to this use must have in effect a substantially linear characteristic throughout a considerable operating range, otherwise modulation of some of the currents by currents of other frequencies is I liable to occur resulting in cross-talk or in other disturbances. According to the invention an amplifiercommonly known as the push-pull? type is arranged to serve as a repeater for all the waves simultaneously. A'repcatcr of this type has the property of transmitting a plurality of frequencies separately and individually without producing their combination frequencies.

The drawing shows a schematic, diagram This procedure is to be understood that other transmitting sets and other receiving could be used in addition to those shown, by connecting them to the line in the manner indicated, andthe invention is not limited to any particular number of such sets or to the par ticular type of transmitters or receivers that are used. Two line sections are indicated by l, 2 and 3, l between which a plurality of conversation currents may be repeated simultaneously in each direction. lime section 1, 2 terminates at each end in line windings for the purpose of connecting to transmitting, receiving or repeating apparatus, and in the net circuits 5 and (5 respectively each of which simulates the characteristics of the line. Line windings 7 and :4 are inductively related to winding 9 through which currents are impressed on the line 1, 2 from genera-tor-modulator sets T and T The set T, comprises a generator 10 of any suitable type for producing an alternating current of carrier frequency (one) which may be a convenient value, preferably several thousand cycles. so as to be near or above the upper limits of audibility. Loupled to the generator is a modulator controlled by the niicri'iphonetrans mitter 12. The modulator shown is the well-known thermionic type consisting of an evacuated chamber in which are a cathode filament 13. an anode ll and a grid 15. A potentiometer resistance 16 with sliding coutact enables the potential impressed on the grid '15 to be regulated. The normal potential oi the'grid is fixed relative to the filament by battery 17 and the batteries 18 and 19-arc respectively for heating the filament i l and furnishing space current. Current Cal of carrier frequency (one) from generator 10 s normally repeated in amplified form 9, 7 and 8 to the line 1, 2.

' variable currents to be induced in the winding 23 in the input of the modulator which voice currents cause the amplitude of the output wave to be varied in a similar-manner. Transmitter T may be of the same' type as T but is adjusted to emit a carrier "wave of different frequency from that genanodes 36 and 37 through the choke erated by T,, which may be designated as carrier frequency (two). The specific transmitting equipment shown forms no part of the present invention, and any other suitable type may be used in place of the particular ones illustrated and described if desired.

Due to the symmetrical character of the coils 7, 8 and 9, and the net 5 at line 1, 2 the current introduced from coil 9 causes no potential diiierence to be set up between the bridging points 24 and 25 as is well known in the art. The filter F in the lineis so proportioned as to pass freely currents of carrier frequency, but to attenuate and substantially extinguish currents of voice frequency, which may have found their way through the modulator directly. 7 Also if the line 1, 2 is used to convey or inary voice currents, together with the carrier currents, the filter F functions in preventing such currents from having access to the receivers on the line 1, 2 that are intended for the carrier current modulations. line 1', 2 is provided with the net circuit 6 for balancing the line as to the transmitted frequencies, and with the usual conjugate coils'26 and'27, to the mid-points of which is connected the bridged coil 28 coupled to the input coil 29 of the repeater circuit. To the terminals of coil 29 are connected the respective grids 30 and 31 of the two-sided amplifier and the mid-point of the coil is connected through a polarizing source 32 to the common connection of the respective filaments 33 and 34; so that a given potential induced in coil 29 varies the potential of grids 30, 31 equally and oppositely. Space current from source 35 is supplied to the respecti ie 1111 e ances 38 and 39 and the variable output liurrents that have been re eated pass through the path containin 'cond nsers 40 and 41 and coil 42 by whic they are impressed. on the outgoing line section 3, a; throu h the windings 43 and 44. By means of t e usual balancing net 45 these outgoing currents are prevented from producing current flow in the bridged coil 46 which is coupled to the input of the amplifier provided for repeating in the op osite direction. Currents incoming over inc 3, 4c, however,-find their waythrough coil 46 and are repeated in the manner entirely similar to that described by The the currents impressed on coils 28 andv 29, and after being amplified are transmitted through coil 47 and coils 26v and. 27 to the line section 1, 2. The repeaters described I are free from selective circuits and are adapted to amplify currents of any desired frequency, and their mode of connection with the line enables simultaneous repeating in both directions.

Receivers R, and R are provided for cooperating with distant transmitting sets which may be similar in general to T, and

T The currents incoming over line 1, 2

sage conveyed on current of carrier frequency (one), and B, may receive that conveyed on current of carrier frequency (two), or the receivers may be made to cooperate with still different carrier frequencies. Receivin set R, is shown as comprising a thermionic detector 52 by which the voice currents which were used to modulate the carrier wave of frequency (two) are detect-' ed and impressed u on the filter which transmits the voice trequency currents to the telephone receiver 53, but prevents the passage of frequencies higher than voicefrequency which may have got through the detector. In similar manner receiving set R, may detect and separate out the message current conveyed on carrier current of frequency (one) and render it receivable by the telephone receiver 54. The articular type of receivers used is immaterial so far as the present invention is concerned, those described being merely for purposes of illustration.

Although the invention has been described and illustrated with reference to a specific preferred embodiment it is to be understood that it is not to be limited to the particular system as a wholp or the specific details, but only to the scope of the appended claims.

What is claimed is:

1. In a carrier wave transmission system a transmission line having considerable attenuation, means for simultaneously generating a plurality of carrier Waves having distinctive frequencies, means for modifying said waves simultanously each in accordance with a different respective signal to be transmitted, a single amplifyin repeater circuit for simultaneously ampli ying all of said signal modified carrier waves, said amplifying repeater circuit comprising a pair of three-element space discharge devices connected in balanced relation with re tions, means for spect to each other whereby the amplifying circuit as a whole has a substantially linear relation between impressed voltages and out-- put current within the operating range, and a single transmission path for conveying the amplified Waves of the different frequencies in common into said transmission line for transmission thereover.

2. In a carrier Wave transmission system a long transmission line divided into sec-- simultaneously generating a plurality, of carrier Waves having distinctive frequencies, means for modulating said waves simultaneously each With speech variations representing a diii'erent conversation to be transmitted and for impressing the resultantmodulated Waves on said line, a single amplifying repeater circuit inserted between two simultaneously amplifying for retransmission over a line section all of said speech 'anced relation with modulated carrier Waves received over the preceding line section, said amplifying circuit comprising a pair of threeelement space discharge respect to each other whereby the-am liiying circuit as a whole has a substantia lylinear relation between impressed voltages and output current with in the operating range, and" means for connecting said repeating circuit to the incomot' the sections of said line for devices Connected in-ba1-' ing and outgoing line sections, said repeating circuit and said connecting means both being free of circuits selective of the individual "waves transmitted.

3. In a carrier Wave transmission system the combination with a long line and terminal ap 'iaratus for simultaneously impressing thereon at a terminal point a 'p1urality of carrier waves of distinctive frequencies modulated in accordance with respective conversational current variations, of an amplifying repeater circuit between the terminals of the line comprising a pair of space discharge tubes of the audion type connected in balanced-relation with respect to each other whereby the amplifying circuit possesses a substantially linear relation between impressed voltages and output currents, and connections for impressing a plurality of the modulated carrier Waves received over a portion of said line upon the repeating circuit for amplification and for impressing the Waves representingsaid plurality of modulated carrier Waves amplified by said repeater circuit upon said line for transmission thereover to a distance.

.In witness whereof, ,I hereunto subscribe my name this thirteenth day of October, A. 1)., 1919. I,

sunron W. KENDALL. 

